Commercial and residential water heaters typically heat water by generating tens of thousands, and even hundreds of thousands, of BTUs. For many years, manufacturers of water heaters have sought to increase the efficiency of the exchange of this heat energy from burned fuel to the water contained in the water heater. Accordingly, maximized heat exchange efficiency has long been sought by commercial and residential water heater manufacturers.
As heat exchange efficiency increases, however, such increased efficiency gives rise to the problems associated with condensation of water vapor from the products of combustion. More specifically, upon burning of a mixture of fuel and air, water is formed as a constituent of the products of combustion. It is recognized that as the temperature of the combustion gases decreases as the result of successful exchange of heat from the combustion gases to water in the water heater, the water vapor within the combustion gases tends to be condensed in greater quantities. In other words, as the temperature of the combustion gases decreases as a direct result of increasingly efficient exchange of heat energy to the water, the amount of condensate forming on the heat exchange surfaces also increases.
Such condensate is typically acidic, with pH values often in the range of between about 2 to 5. The formation of increased amounts of such acidic condensate, even in relatively small quantities, can accelerate the corrosion of heat exchange tubing, increase oxidation and scale formation, reduce heat exchange efficiency and contribute to failure of the water heater.
Commercial and residential water heaters can be designed to operate below the efficiencies at which increased quantities of condensate are likely to form (i.e., below the condensing mode) so that acidic products of combustion are discharged in vapor form in higher temperature exhaust gas. To do so, however, compromises the efficiency of the water heater.
Accordingly, there continues to be a need to manage one or more of these problems associated with the condensation formed by condensing water heaters.